1. Field of the Invention
The present disclosure relates to an image forming apparatus.
2. Description of the Related Art
An image forming apparatus that uses an electrographic system such as a copier, printer, a facsimile device, or a multi-functional peripheral thereof forms a toner image by using a developing device to supply toner containing in developer to the surface of a photoreceptor on which an electrostatic latent image based on image data is formed. The toner image formed on the photoreceptor is subsequently transferred to a sheet by using a transfer device or the like. Then, by using a fixing device to pressurize and heat the toner image that was transferred on the sheet, the toner image is fixed to the sheet and image based on the image data is thereby formed on the sheet.
This kind of image forming apparatus is demanded of faster speed and higher quality, and lower printing cost; for instance, the reduction in printing cost that is required per single sheet of paper. In order to achieve the reduction of printing cost, considered may be achieving the longer service life of consumable supplies and reduction of consumable supplies cost. As the foregoing consumable supplies cost, it is known that sophisticated members such as the photoreceptor and developer account for most of the cost.
Foremost, as the photoreceptor that is provided to an electrographic image forming apparatus, there is an organic photoreceptor including a photosensitive layer containing, as its main component, organic materials such as binder resin, a charge generation agent and a charge transfer agent, or an inorganic photoreceptor including a photosensitive layer made of inorganic materials such as amorphous silicon or selenium. In order to achieve the longer service life of the photoreceptor, in the case of an organic photoreceptor, measures for preventing the phenomenon where the photosensitive layer is scraped; that is, drum scraping, are being taken by providing a protective layer on the surface of the photosensitive layer. Moreover, in the case of an inorganic photoreceptor; for example, an amorphous silicon photoreceptor in which the photosensitive layer is amorphous silicon, the abrasion resistance of the photosensitive layer is sufficiently high, and it is possible to sufficiently inhibit the scraping of the photosensitive layer. Based on the above, the longer service life of the amorphous silicon photoreceptor has been achieved, and the life of the photoreceptor is now equal to or longer than the life of the image forming apparatus as a machine; that is, the so-called machine life. The longer service life of the photoreceptor is beneficial for reducing the consumable supplies cost.
Moreover, as the developer that is used in an electrographic image forming apparatus, there is mono-component developer that contains toner but does not contain carrier, or two-component developer that contains toner and carrier. The developing device that is provided in an electrographic image forming apparatus agitates the developer in advance and charges the toner prior to supplying the toner to the surface of the photoreceptor. Here, if the two-component developer is used as the developer, the toner is agitated under the existence of the carrier when the developer is agitated. Meanwhile, if the mono-component developer is used as the developer, only the toner is agitated. Accordingly, the developing device using the two-component developer can ensure the charged amount of the toner more easily in comparison to the developing device using the mono-component developer.
In addition, under normal circumstances, the developing device using the two-component developer; for example, a two-component developing device foremost causes the two-component developer to come in contact with the development roller that is disposed opposite to the photoreceptor upon performing image formation. Consequently, since a magnet is included in the development roller, the carrier lies in the shape of brushes on the development roller. Since the toner is attached on the carrier, a magnetic brush made from the two-component developer is formed. By causing the magnetic brush to come in contact with or be in close proximity to the photoreceptor, the toner is supplied to the surface of the photoreceptor on which the electrostatic latent image based on image data was formed, and the toner image based on the image data is thereby formed. As described above, since the toner is used when the two-component developing device performs image formation, new toner is supplied (replenished) to perform image formation over a long period of time. Meanwhile, since the carrier is not used, the same carrier is repeatedly used even when image formation is performed over a long period of time.
In the case of the developing device using the two-component developer, as described above, in comparison to the developing device using the mono-component developer, it is easier to ensure the charged amount of the toner and obtain a high quality image as the formed image. Nevertheless, when the developing device using the two-component developer performs image formation over a long period of time, the carrier will be repeatedly used for a long period of time, and it is known that the performance of the carrier, such as charge application performance, will deteriorate. Consequently, it is known that the charged amount of the toner will decrease, which tends to cause fogging and the like, and becomes difficult to form a favorable image.